Archive

Fruit and nut trees, like these in a Yolo County walnut orchard, need a certain amount of cold weather each year for proper foliage and flower development. As the climate warms, declining annual chill hours — the total number of hours when the temperature falls between 32°F and 45°F — may change where crops are grown.Photo by Will Suckow

Editor Jim Downing talks about what's in the current issue of California Agriculture journal — wild horses, the economics of beef, groundwater in California and more.

Peer-reviewed research and review articles

A century of climate data and six decades of crop acreage data in Yolo County are used to analyze climate–crop acreage trends and predict future acreages.

The impacts of climate change on agriculture depend on local conditions and crops grown. For instance, warmer winter temperatures in a given area would reduce chill hours, potentially cutting yields for some crops but extending the growing season for others. Using a century of climate data and six decades of acreage data, we established quantitative economic relationships between the evolution of local climate and acreage of 12 important crops in Yolo County. We then used the historical trend in climate change to project future crop acreages in the county. Only marginal changes in acreage in 2050 were projected for tree and vine crops there, in part because chill hours, although lower, remained above critical values. Walnuts were the most vulnerable tree crop, and the projections indicated some cultivars might be marginal in years with particularly warm winters. Processing tomato acreage might increase, due to a longer growing season, and also alfalfa acreage, if water availability and other factors remain constant.

California researchers are assessing the suitability of beneficial natural enemies,
including Trissolcus japonicus, an egg parasitoid from China, to control BMSB.

Brown marmorated stink bug (BMSB) is an invasive, polyphagous pest that has been detected
in 42 U.S. states. In 2010, it caused millions of dollars in crop damages to apple
growers on the East Coast, where it arrived from Asia during the 1990s. In 2002, BMSB
was reported in California; since then, it has been detected in 28 counties and is
established in at least nine counties. Although this pest has not yet been found on
commercial crops in the state, detections of BMSB in commercial orchards have been
documented in Oregon and Washington. Proactive research in California has joined national
efforts led by U.S. Department of Agriculture researchers to develop a classical biological
control program for BMSB. A study is under way to determine potential non-target effects
of a specialist egg parasitoid, Trissolcus japonicus (Hymenoptera: Platygastridae), imported from Beijing, China, part of the home range
of BMSB. In addition, the role of BMSB natural enemies residing in California is being
assessed. A review of the recent research outlines the possible opportunities for
reducing the threat BMSB poses to California.

Cherry growers are advised to monitor outside their orchards as well as within them,
and to count both male and female flies in the traps.

The spotted wing drosophila, first detected in California in 2008, has become a major
insect pest in caneberries and sweet cherries, causing commercial crop losses. Managing
it is challenging because it has many other hosts, including riparian and backyard
fruit plantings, and it increases rapidly, with generations overlapping one another.
In our study we monitored trap captures in two parts of the San Joaquin Valley, within
sweet cherry orchards and in nearby locations. Captures of adult flies showed two
main periods of activity — spring and fall — and low captures in the winter (except
for citrus and evergreen riparian areas) and summer. On many occasions during the
year, trap captures were higher outside of the cherry orchards than within them. Additionally,
early in the season, when decisions about control programs are being made, the sex
ratio of captured flies in cherries was strongly female-biased. The results suggest
that during the weeks leading up to harvest growers should experiment by placing traps
in different environments surrounding their orchards to determine SWD activity and
potential pest pressure locally, and monitor for both male and female flies.

Equations that describe the nonlinear saturation process for standard monitoring traps can help growers interpret trap data and better estimate NOW populations.

Trapping is an essential tool used to decide the need for and/or timing of an insecticide application. The assumption is that the information is accurate, but accuracy is dependent on trap reliability and efficacy. One factor that affects reliability is trap saturation, defined as the measurable decrease in trap capture due to reduced trapping effectiveness caused by the accumulation of insects already in a trap. In this study, we used unmated female navel orangeworm (NOW, Amyelois transitella (Walker)) as sex pheromone baits in wing traps that varied by color and glue/trapping surface in order to evaluate saturation thresholds and quantify trap effectiveness. Effectiveness decreased in each type of sticky trap as the number of insects caught increased, because of the accumulation of scales and insect bodies on the glue surface. The continued accumulation of insects further reduced trap capture, and this decrease in capture could be described by a regression using a power transformation. The resulting saturation equations that we calculated will help pest control advisers and growers interpret their trap data by better estimating the relationship between the number of males trapped versus those that visited the trap.

A review of blue gum in California suggests that management efforts must be region-specific and consider native plants and animals, as well as social factors.

Blue gum eucalyptus (Eucalyptus globulus) is a large tree native to Australia that was widely planted throughout California for reforestation, building and timber, but in some areas has spread beyond its planted borders and substantially altered wildlands. Due to its fast growth, large size and reproductive potential, blue gum's impacts on native vegetation, wildlife and ecosystem processes are of concern, particularly in areas with reliable year-round rainfall or fog, where it is most likely to spread. Depending on levels of invasion and rate of spread, blue gum may have negative, positive or neutral impacts on fire regimes, water and nutrient availability, understory vegetation and higher trophic levels. Additional research on the abiotic and biotic impacts of blue gum, quantitative estimates of area covered by blue gum, and weed risk assessments that allow for region-specific climatic information and management goals to be incorporated are needed to guide management of blue gum populations.

Fruit and nut trees, like these in a Yolo County walnut orchard, need a certain amount of cold weather each year for proper foliage and flower development. As the climate warms, declining annual chill hours — the total number of hours when the temperature falls between 32°F and 45°F — may change where crops are grown.Photo by Will Suckow

Editor Jim Downing talks about what's in the current issue of California Agriculture journal — wild horses, the economics of beef, groundwater in California and more.

Peer-reviewed research and review articles

A century of climate data and six decades of crop acreage data in Yolo County are used to analyze climate–crop acreage trends and predict future acreages.

The impacts of climate change on agriculture depend on local conditions and crops grown. For instance, warmer winter temperatures in a given area would reduce chill hours, potentially cutting yields for some crops but extending the growing season for others. Using a century of climate data and six decades of acreage data, we established quantitative economic relationships between the evolution of local climate and acreage of 12 important crops in Yolo County. We then used the historical trend in climate change to project future crop acreages in the county. Only marginal changes in acreage in 2050 were projected for tree and vine crops there, in part because chill hours, although lower, remained above critical values. Walnuts were the most vulnerable tree crop, and the projections indicated some cultivars might be marginal in years with particularly warm winters. Processing tomato acreage might increase, due to a longer growing season, and also alfalfa acreage, if water availability and other factors remain constant.

California researchers are assessing the suitability of beneficial natural enemies,
including Trissolcus japonicus, an egg parasitoid from China, to control BMSB.

Brown marmorated stink bug (BMSB) is an invasive, polyphagous pest that has been detected
in 42 U.S. states. In 2010, it caused millions of dollars in crop damages to apple
growers on the East Coast, where it arrived from Asia during the 1990s. In 2002, BMSB
was reported in California; since then, it has been detected in 28 counties and is
established in at least nine counties. Although this pest has not yet been found on
commercial crops in the state, detections of BMSB in commercial orchards have been
documented in Oregon and Washington. Proactive research in California has joined national
efforts led by U.S. Department of Agriculture researchers to develop a classical biological
control program for BMSB. A study is under way to determine potential non-target effects
of a specialist egg parasitoid, Trissolcus japonicus (Hymenoptera: Platygastridae), imported from Beijing, China, part of the home range
of BMSB. In addition, the role of BMSB natural enemies residing in California is being
assessed. A review of the recent research outlines the possible opportunities for
reducing the threat BMSB poses to California.

Cherry growers are advised to monitor outside their orchards as well as within them,
and to count both male and female flies in the traps.

The spotted wing drosophila, first detected in California in 2008, has become a major
insect pest in caneberries and sweet cherries, causing commercial crop losses. Managing
it is challenging because it has many other hosts, including riparian and backyard
fruit plantings, and it increases rapidly, with generations overlapping one another.
In our study we monitored trap captures in two parts of the San Joaquin Valley, within
sweet cherry orchards and in nearby locations. Captures of adult flies showed two
main periods of activity — spring and fall — and low captures in the winter (except
for citrus and evergreen riparian areas) and summer. On many occasions during the
year, trap captures were higher outside of the cherry orchards than within them. Additionally,
early in the season, when decisions about control programs are being made, the sex
ratio of captured flies in cherries was strongly female-biased. The results suggest
that during the weeks leading up to harvest growers should experiment by placing traps
in different environments surrounding their orchards to determine SWD activity and
potential pest pressure locally, and monitor for both male and female flies.

Equations that describe the nonlinear saturation process for standard monitoring traps can help growers interpret trap data and better estimate NOW populations.

Trapping is an essential tool used to decide the need for and/or timing of an insecticide application. The assumption is that the information is accurate, but accuracy is dependent on trap reliability and efficacy. One factor that affects reliability is trap saturation, defined as the measurable decrease in trap capture due to reduced trapping effectiveness caused by the accumulation of insects already in a trap. In this study, we used unmated female navel orangeworm (NOW, Amyelois transitella (Walker)) as sex pheromone baits in wing traps that varied by color and glue/trapping surface in order to evaluate saturation thresholds and quantify trap effectiveness. Effectiveness decreased in each type of sticky trap as the number of insects caught increased, because of the accumulation of scales and insect bodies on the glue surface. The continued accumulation of insects further reduced trap capture, and this decrease in capture could be described by a regression using a power transformation. The resulting saturation equations that we calculated will help pest control advisers and growers interpret their trap data by better estimating the relationship between the number of males trapped versus those that visited the trap.

A review of blue gum in California suggests that management efforts must be region-specific and consider native plants and animals, as well as social factors.

Blue gum eucalyptus (Eucalyptus globulus) is a large tree native to Australia that was widely planted throughout California for reforestation, building and timber, but in some areas has spread beyond its planted borders and substantially altered wildlands. Due to its fast growth, large size and reproductive potential, blue gum's impacts on native vegetation, wildlife and ecosystem processes are of concern, particularly in areas with reliable year-round rainfall or fog, where it is most likely to spread. Depending on levels of invasion and rate of spread, blue gum may have negative, positive or neutral impacts on fire regimes, water and nutrient availability, understory vegetation and higher trophic levels. Additional research on the abiotic and biotic impacts of blue gum, quantitative estimates of area covered by blue gum, and weed risk assessments that allow for region-specific climatic information and management goals to be incorporated are needed to guide management of blue gum populations.